1. Field of the Invention
This invention relates to an image forming apparatus comprising an upper casing which is swingable on a fulcrum shaft and is mounted on a lower casing which is provided with a copy material transport means and movable scanning means disposed within the upper casing.
2. Description of the Related Art
The image forming apparatuses of the above stated kind include an apparatus which is arranged as shown in FIG. 1 of the accompanying drawings. This is a copier having a copy-board 101 secured to the upper casing 106. With an original 103 placed on the copy-board 101, an image corresponding to the image of the original 103 is formed on a recording material (or copy paper) 104 in accordance with a known electro-photographic method by moving a scanning optical system 102 along rails in the direction of arrow A or B to have the original 103 exposed to light from the optical system 102. The apparatus main body consists of the upper casing 106 and a lower casing 107. To facilitate replacement work on a photosensitive member drum 105, maintenance or inspection work and work to take out the recording material 104 in the event of the occurrence of a jam, which is a typical problem when transporting the recording material 104, the upper casing 106 is arranged to be swingable to open and close on a fulcrum shaft 108 relative to the lower casing 107. The arrangement is such that, when the upper casing 106 is opened, the scanning optical system 102, which is arranged within the upper casing 106 is lifted up to expose to the outside the recording material transport passage, etc. which is disposed within the lower casing 107.
The conventional apparatus mentioned above has been arranged such that, in the event of the occurrence of a jam during a transport action on the recording material or copy paper 104, the transporting process, the movement of the scanning optical system 102 and the action of the photosensitive member drum 105 are brought to a stop and a jam display is made by means of a lamp or the like. Therefore, when the upper casing 106 is opened for removal of the recording material 104 after a jam occurred during the process of scanning by the scanning optical system 102 and with the original thus stopped from being scanned, the scanning optical system 102 slides down by its own weight in the direction of arrow A along the rails and comes to a stop colliding with a rail end member. This has presented a problem since a mirror of the scanning optical system tends to be dislodged from its set angular position by the impact and a lamp or a reflector of the optical system tends to be also dislodged and damaged.
To solve this problem, therefore, a method for preventing the scanning optical system 102 from sliding down by locking it with a lock member when the upper casing 106 is opened has been proposed, for example, in Japanese Patent Publication No. SHO 59-3735. It is another conceivable solution of this problem to make the scanning optical system 102 less slidable over the rails. However, the former solution necessitates the lock member to be arranged to operate in association with the opening movement of the upper casing 106 which requires a complex arrangement and thus incurs an increase in cost. As to the latter solution of making the rails less slidable, it requires a greater driving force on the scanning optical system for the process of effecting an exposure which not only causes an increase in electrical energy consumption but also deteriorates the quality of images formed because of unsmooth scanning.
Meanwhile, Japanese Laid-Open Patent Application No. SHO 55-153949 and U.S. Pat. No. 4,432,639 have disclosed a copier which is provided with lock means. The lock means is arranged to allow the upper casing to be lifted up only after the copy-board is manually moved to a part of the upper casing which is located on the lower side of the upper casing when the upper casing is rotated upward. However, that arrangement is inconvenient for an operator who is either unaware of or has forgotten that the upper casing cannot be lifted up unless the copy-board is moved in one direction beforehand. The operator then tends to try to lift the upper casing by force when he or she sees the light of a jam display which might break the apparatus.
U.S. Pat. No. 4,312,587 discloses a copier which is arranged to have the scanning optical system move to a given position in the event of a jammed state. However, that disclosure fails to include any arrangement necessary for opening and closing the upper casing by rotating the upper casing relative to the lower casing.